Organoborane polyoxyalkylenepolyamine complexes and adhsesive compositions made therewith

ABSTRACT

A complex comprises organoborane and polyoxyalkylenepolyamine. The complexes are useful in systems for initiating the polymerization of acrylic monomer, which systems further include an amine reactive compound. Polymerizable acrylic monomer compositions useful as adhesives can be prepared.

This is a division of application Ser. No. 08/422,429 filed Apr. 14,1995 now U.S. Pat. No. 5,621,143.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to organoborane polyamine complexesand, more specifically, to such complexes that incorporatepolyoxyalkylenepolyamines. The invention further relates to the use ofthese complexes in systems for initiating the polymerization of acrylicmonomers, as well as acrylic adhesive compositions made therewith. Theadhesive compositions have excellent adhesion to a variety ofsubstrates, especially low surface energy polymers.

2. Description of the Related Art

Organoboranes such as tributylborane and triethylborane have beenreported to initiate and catalyze the polymerization of vinyl monomers(see, for example, G. S. Kolesnikov et al., Bull. Acad. Sci. USSR, Div.Chem. Sci. 1957, p. 653; J. Furakawa et al., Journal of Polymer Science,volume 26, issue 113, p. 234, 1957; and J. Furakawa et al., Journal ofPolymer Science, volume 28, issue 116, 1958). The organoborane compoundsof the type described in these references are known to be quitepyrophoric in air which complicates facile use.

Chemical Abstracts No. 134385q (volume 80, 1974) "Bonding Polyolefin orVinyl Polymers" reports that a mixture of 10 parts methyl methacrylate,0.2 part tributylborane, and 10 parts poly(methylmethacrylate) was usedto bond polyethylene, polypropylene and poly(vinyl acetate) rods.

U.S. Patent No. 3,275,611 to E. H. Mottus et al. discloses a process forpolymerizing olefinic compounds with a catalyst comprising anorganoboron compound, a peroxygen compound, and an amine. Theorganoboron compound and the amine may be added to the reaction mixtureseparately or they may be added as a preformed complex. The latterapproach reportedly has the advantage of making the boron compound moreeasily handled, especially for certain boron compounds that tend to bepyrophoric in air but which are not pyrophoric when complexed.Especially useful boron catalysts are said to have the following generalformulas: R₃ B, RB(OR)₂, R₂ B(OR), R₂ BOBR₂, R₂ BX, and R₂ BH, where Ris preferably an alkyl radical having from 1 to 10 or more carbon atoms,and X is a halogen. Various amine complexing agents are mentionedalthough pyridine, aniline, toluidine, dimethylbenzylamine, and nicotineare used in the examples.

While Mottus et al. refer to polymerizing methacrylate monomers, thereis no indication that the resulting polymers are useful as adhesives.Various acids are mentioned as monomers that may be polymerized butthere is no indication that an acid is a component of the polymerizationinitiator system.

British Patent Specification No. 1,113,722 "Aerobically PolymerisableCompositions," published May 15, 1968 discloses the polymerization ofacrylate monomers through the use of a free-radical catalyst (e.g.,peroxides) and triarylborane complexes having the general formula (R)₃B-Am wherein R is an aryl radical having from 6 to 12 carbon atoms andAm is an amine that can be selected from various classes such asalkylamines, cycloalklyamines, aralklyamines, polyamines (e.g., alkylenediamines and triamines), and heterocyclic amines. The polymerization isactivated by heat or the addition of an acid. The resulting compositionsare reportedly useful as adhesives.

Chemical Abstracts No. 88532r (volume 73, 1970) "Dental Self-curingResin" and the full text paper to which it refers report thattributylborane can be made stable in air by complexing it with ammoniaor certain amines (e.g., aniline, n-butylamine, piperidine,ethylenediamine) at a mole ratio of one and that the tributylborane canbe reactivated with an amine acceptor such as an isocyanate, an acidchloride, a sulfonyl chloride, or anhydrous acetic acid. As a result,the complex can be used to polymerize blends of methyl methacrylate andpoly(methylmethacrylate) to provide a dental adhesive.Tributylborane-ethylenediamine complexes and triethylborane-ammoniacomplexes, each with p-toluenesulfonyl chloride as the amine acceptor,are specifically mentioned.

A series of patents issued to Skoultchi and Skoultchi et al. (U.S. Pat.Nos. 5,106,928, 5,143,884, 5,286,821, 5,310,835, and 5,376,746) disclosea two part initiator system that is reportedly useful in acrylicadhesive compositions, especially elastomeric acrylic adhesives. Thefirst part of this two part system includes a stable organoborane aminecomplex and the second part includes a destabilizer or activator such asan organic acid or an aldehyde. The organoborane compound of the complexhas the general formula: ##STR1## where R, R₁ and R₂ are either alkylgroups having 1 to 10 carbon atoms or phenyl groups. Useful aminesinclude n-octylamine, 1,6-diaminohexane, diethylamine, dibutylamine,diethylenetriamine, dipropylenediamine, 1,3-propylenediamine, and1,2-propylenediamine.

The adhesive compositions are reportedly particularly useful instructural and semi-structural applications such as speaker magnets,metal-metal bonding, (automotive) glass-metal bonding, glass-glassbonding, circuit board component bonding, selected plastic to metal,glass, wood, etc. bonding, and electric motor magnets. Those plasticsthat may be bonded are not further described.

An efficient, effective means for adhesively bonding low surface energyplastic substrates such as polyethylene, polypropylene andpolytetrafluoroethylene (e.g., TEFLON) has long been sought. Thedifficulties in adhesively bonding these materials are well known. See,for example, "Adhesion Problems at Polymer Surfaces" by D. M. Brewisthat appeared in Progress in Rubber and Plastic Technology, volume 1,page 1 (1985). The conventional approaches typically function by: (1)increasing the surface energy of the substrate (to more closely matchthe surface energies of the substrate and the adhesive thereby promotingbetter wetting of the substrate by the adhesive) and/or (2) eliminatingadditives and low molecular weight polymer fractions in the substratethat can migrate to the substrate surface and adversely affect adhesionby forming a weak boundary layer.

As a result, the conventional approaches often use complex and costlysubstrate surface preparation techniques such as flame treatment, coronadischarge, plasma treatment, oxidation by ozone or oxidizing acids, andsputter etching. Alternatively, the substrate surface may be primed bycoating it with a high surface energy material. However, to achieveadequate adhesion of the primer, it may be necessary to first use thesurface preparation techniques described above. All of these techniquesare well known, as reported in Treatise on Adhesion and Adhesives (J. D.Minford, editor, Marcel Dekker, 1991, New York, volume 7, pages 333 to435). The known approaches are frequently customized for use withspecific substrates. As a result, they may not be useful for bonding lowsurface energy plastic substrates generally.

Moreover, the complexity and cost of the presently known approaches donot render them particularly suitable for use by the retail consumer(e.g., home repairs, do-it-yourselfers, etc.) or in low volumeoperations. One vexing problem is the repair of many inexpensiveeveryday household articles that are made of polyethylene, polypropyleneor polystyrene such as trash baskets, laundry baskets and toys.

Consequently, there has been a considerable and long felt need for asimple, easy to use adhesive that can readily bond a wide variety ofsubstrates, especially low surface energy materials, such aspolyethylene, polypropylene and polytetrafluoroethylene, withoutrequiring complicated surface preparation, priming and the like. Itwould also be considered useful for the adhesive to be able to bond awide variety of diverse surfaces, including metals.

While an adhesive that can bond low surface energy plastics is certainlyadvantageous, the commercial utility of such an adhesive would beenhanced if the components thereof could be combined in a convenient mixratio. This would permit facile application of the adhesive usingconventional adhesive dispensers without the need for laborious handweighing and mixing of the different components. However, the convenientmix ratio should not come at the expense of significantly reducedstorage stability or performance. Thus, there is not only a need for anadhesive that can bond low surface energy plastics, but a need for suchan adhesive that can be readily blended in a convenient mix ratiowithout a material reduction in storage stability or performance.

SUMMARY OF THE INVENTION

The invention relates to organoborane polyamine complexes and, moreparticularly, to such complexes that include polyoxyalkylenepolyamine.The complexes can be used in systems that initiate the polymerization ofacrylic monomer to yield acrylic adhesive compositions. The acrylicadhesive compositions have excellent adhesion to a wide variety ofsubstrates but are especially useful for bonding low surface energyplastics (e.g., polyethylene, polypropylene, polytetrafluoroethylene,etc.) that, heretofore, have been bonded using complex and costlysurface preparation techniques.

In general, complexes of the invention comprise organoborane andpolyoxyalkylenepolyamine. The organoborane polyamine complexes have thegeneral structure: ##STR2## wherein Am is polyoxyalkylenepolyamine andhas a structure selected from the group consisting of H₂ NR⁴ O--(R⁵O)_(w) --(R⁶ O)_(x) --(R⁵ O)_(y) --R⁴ NH₂ (I) and H₂ NR⁴ O--(R⁵ O)_(w)!_(z) --R⁷ (II).

In this structure, R¹ is preferably an alkyl group having 1 to 10 carbonatoms, and R² and R³ are independently selected from alkyl groups having1 to 10 carbon atoms and phenyl-containing groups. More preferably, R¹,R² and R³ are alkyl groups having 1 to 5 carbon atoms. Most preferably,R¹, R² and R³ are the same.

R⁴, R⁵ and R⁶ are preferably alkylene groups having 1 to 10 carbon atomsand which may be the same or which may be different. More preferably, R⁴is an alkyl group having 2 to 4 carbon atoms, R⁵ is an alkyl group of 2or 3 carbon atoms, and R⁵ is an alkyl group of 2 or 3 carbon atoms. R⁷is a residue of a poylol.

The value of w is ≧1 (more preferably about 1 to 150, and mostpreferably about 1 to 20). The value of x and y are ≧0. The value of zis >2 (more preferably 3 or 4). The values for w, x, y and z arepreferentially selected such that the complex is a liquid at roomtemperature. Consequently, the molecular weight of thepolyoxyalkylenepolyamine is less than about 5,000, more preferably about1,000 or less, and most preferably about 250 to 1,000.

The value of v is selected so as to provide an effective ratio ofnitrogen atoms to boron atoms in the complex. In complexes employingpolyoxyalkylenepolyamine (I), the value of v may broadly vary over therange of about 0.1 to 2. In complexes employing polyoxyalkylenepolyamine(II), the value of v may broadly vary over the range of about 0.1 to z.The ratio of nitrogen atoms to boron atoms in the complex should beabout 1:1 to 4:1, preferably about 1:1 to 2:1, more preferably about 1:1to 1.5:1, and most preferably about 1:1.

Organoborane polyamine complexes of the invention can be used in systemsthat are capable of initiating the polymerization of an acrylic monomer.In addition to organoborane polyamine complexes such as those describedabove, these systems further comprise an effective amount of a compoundthat is reactive with amine for liberating the organoborane. A widevariety of amine reactive compounds may be used including isocyanates,acids, acid chlorides, sulfonyl chlorides, and aldehydes. Useful acidsinclude Lewis acids and Bronsted acids, although acrylic acid andmethacrylic acid are preferred. The amount of amine reactive compound ispreferentially stoichiometric with the equivalents of amine but largeramounts may be used, for example, twice stoichiometric. Where an acidprovides the amine reactive compound, a useful amount is in the range ofabout 100 to 350 mole %, more preferably about 150 to 250 mole %.

Consequently, the invention also relates to a polymerizable acryliccomposition that comprises at least one acrylic monomer, an effectiveamount of an organoborane polyamine complex of the invention, and aneffective amount of a compound that is reactive with amine (such asthose described above) for liberating the organoborane to initiatepolymerization of the at least one acrylic monomer.

A wide variety of acrylic monomers may be used but those which arepreferred include monofunctional acrylate ester, monofunctionalmethacrylate ester, substituted derivatives of the foregoing, and blendsof the foregoing. Methacrylate esters are especially useful,particularly desirable examples of which include methyl methacrylate,ethyl methacrylate, methoxy ethyl methacrylate, hydroxyethylmethacrylate, hydroxypropyl methacrylate, cyclohexyl methacrylate,tetrahydrofurfuryl methacrylate, and blends thereof. Blends of alkylmethacrylate (e.g., methyl methacrylate) and alkyl acrylate (especiallythose in which the alkyl group has from 4 to 10 carbon atoms, e.g.,butyl acrylate) are also quite useful.

Acrylic compositions of the invention are uniquely useful in providingadhesives, and adhesive compositions of the invention provide excellentadhesion to low surface energy polymeric or plastic substrates thathistorically have been very difficult to bond. Adhesion to low surfaceenergy polymeric substrates is enhanced when the adhesive compositioncomprises about 0.03 to 1.5 weight % boron, more preferably about 0.1 to0.3 weight % boron.

Consequently, in another aspect, the invention relates to a compositearticle comprising a first substrate, and a second substrate bonded tothe first substrate by an acrylic adhesive composition according to theinvention. Either or both substrates may be a low surface energy polymeror plastic such as polyethylene, polypropylene orpolytetrafluoroethylene.

In another aspect, the invention relates to a method of initiating thepolymerization of an acrylic monomer, the method comprising the steps ofproviding at least one acrylic monomer, blending the at least oneacrylic monomer with a polymerization initiator system according to theinvention, and initiating polymerization of the at least one acrylicmonomer.

The invention further relates to a method of bonding a low surfaceenergy polymer to a substrate. The method comprises the steps ofproviding a low surface energy polymer, providing a substrate, providingan adhesive composition according to the invention, applying theadhesive composition to either the low surface energy polymer or thesubstrate, joining the low surface energy polymer and the substrate withthe adhesive composition therebetween, and permitting the adhesivecomposition to cure to adhesively bond the low surface energy polymerand the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a broad aspect, this invention relates to organoborane polyaminecomplexes, particularly those complexes that are made frompolyoxyalkylenepolyamine. The complexes are especially useful inproviding systems for initiating the polymerization of acrylic monomer.Acrylic adhesives can be produced using the organoborane polyaminecomplexes of the invention. The acrylic adhesives can bond a widevariety of substrates, but provide exceptionally good adhesion to lowsurface energy plastic substrates (e.g., polyethylene, polypropylene,polytetrafluoroethylene, etc.) that, heretofore, have been bonded usingcomplex and costly surface preparation techniques.

The complexes of the invention are complexes of organoborane andpolyoxyalkylenepolyamine. They preferably have the following generalstructure: ##STR3## where R¹ is an alkyl group having 1 to 10 carbonatoms, and R² and R³ are independently selected from alkyl groups having1 to 10 carbon atoms and phenyl-containing groups. More preferably, R¹,R² and R³ are alkyl groups having 1 to 5 carbon atoms such as methyl,ethyl, propyl, iso-propyl, n-butyl, iso-butyl, and pentyl. In general,shorter carbon chain lengths are preferred for the R¹, R² and R³ groupsas this promotes enhanced stability of the complex in air. Smaller, lessbulky substituents are also preferred as larger, more bulky groups maynegatively affect the adhesion provided by adhesives made therewith. By"independently selected" it is meant that R² and R³ may be the same orthat they may be different. R¹ may be the same as R² or R³, or it may bedifferent. Preferably R¹, R² and R³ are the same. Most preferred arecomplexes in which R¹, R² and R³ are each ethyl groups.

"Am" represents the polyoxyalkylenepolyamine portion of the complex andmay be selected from the following structures:

    H.sub.2 NR.sup.4 O--(R.sup.5 O).sub.w --(R.sup.6 O).sub.x --(R.sup.5 O).sub.y --R.sup.4 NH.sub.2                               (I)

(i.e., polyoxyalkylene diamines) or

     H.sub.2 NR.sup.4 O--R.sup.5 O).sub.w !.sub.z --R.sup.7    (II).

Blends of different polyoxyalkylenepolyamines may also be used. R⁴, R⁵and R⁶ are alkylene groups having 1 to 10 carbon atoms and may be thesame or may be different. Preferably, R⁴ is an alkyl group having 2 to 4carbon atoms such as ethyl, n-propyl, iso-propyl, n-butyl or iso-butyl.Preferably, R⁵ is an alkyl group having 2 or 3 carbon atoms such asethyl, n-propyl or iso-propyl. Preferably, R⁶ is an alkyl group having 2or 3 carbon atoms such as ethyl, n-propyl or iso-propyl. R⁷ is theresidue of a polyol used to prepare the polyoxyalkylenepolyamine(i.e.,the organic structure that remains if the hydroxyl groups are removed).R⁷ may be branched or linear, saturated or unsaturated, and substitutedor unsubstituted (although any substituents should not interfere withoxyalkylation reactions). Residues that are branched, saturated and/orunsubstituted are preferred.

The value of w is ≧1, more preferably about 1 to 150, and mostpreferably about 1 to 20. Structures in which w is 2, 3 or 4 are usefultoo. The value of x and y are both ≧0. The value of z is >2, morepreferably 3 or 4 (so as to provide, respectively, polyoxyalkylenetriamines and tetraamines). The selection of values for w, x, y and zinfluences the physical form of the complex and the molecular weight ofthe polyoxyalkylenepolyamine. It is preferred that the values of w, x, yand z be chosen such that the resulting complex is a liquid at roomtemperature as this simplifies handling and mixing thereof. Usually, thepolyoxyalkylenepolyamine is itself a liquid. Lower molecular weightpolyoxyalkylenepolyamines are also preferred in order to promotesolubility of the complex in compositions made therewith and to enhancethe performance of ultimate compositions that incorporate the complex.Molecular weights of less than about 5,000 may be used, althoughmolecular weights of about 1,000 or less are more preferred, andmolecular weights of about 250 to 1,000 are most preferred.

Examples of particularly preferred polyoxyalkylenepolyamines includepolyethyleneoxidediamine, polypropyleneoxidediamine,polypropyleneoxidetriamine, diethyleneglycolpropylenediamine,triethyleneglycolpropylenediamine, polytetramethyleneoxidediamine,polyethyleneoxide-co-polypropyleneoxidediamine, andpolyethyleneoxide-co-polyproyleneoxidetriamine.

Examples of suitable commercially available polyoxyalkylenepolyaminesinclude various JEFFAMINES from Huntsman Chemical Company such as the D,ED, and EDR series diamines (e.g., D-400, D-2000, D-5000, ED-600,ED-900, ED-2001, and EDR-148), and the T series triamines (e.g., T-403),as well as H221 from Union Carbide Company.

The value of v is selected so as to provide an effective ratio ofnitrogen atoms to boron atoms in the complex, as explained more fullyhereinbelow. For polyoxyalkylenepolyamine I, the value of v ispreferably in the range of about 0.1 to 2. For polyoxyalkylenepolyamineII, the value of v is preferably in the range of about 0.1 to z, thevalue of z for any particular complex providing the upper boundary ofthe preferred range for v. For polyoxyalkylenepolyamine II, the value ofv is preferably 3 or 4 when z is, respectively, 3 or 4.

Highly preferred organoborane polyamine complexes according to theinvention include triethylborane complexed with any of the "particularlypreferred" polyoxyalkylenepolyamines mentioned above.

The nitrogen atom to boron atom ratio in the complex is broadly about1:1 to 4:1. Preferably, however, the ratio is about 1:1 to 2:1, morepreferably about 1:1 to 1.5:1, and most preferably about 1:1. A nitrogenatom to boron atom ratio of less than 1:1 leaves free organoborane, amaterial that tends to be pyrophoric. At nitrogen atom to boron atomratios in excess of 2:1, the practical utility of the complex in, forexample, an adhesive system diminishes as the amount of complex thatmust be employed to generate a useful adhesive becomes larger. Inaddition, at high nitrogen atom to boron atom ratios, the amount ofagent that must be added to react with the polyamine so as to liberateorganoborane (to initiate polymerization) also becomes larger. Theadditional reactants could complicate the adhesive system.

The organoborane polyamine complex is employed in an effective amount,which is an amount large enough to permit polymerization to readilyoccur to obtain a polymer (preferably, an acrylic polymer) of highenough molecular weight for the desired end use. If the amount oforganoborane polyamine complex is too low, then the polymerization maybe incomplete or, in the case of adhesives, the resulting compositionmay have poor adhesion. On the other hand, if the amount of organoboranepolyamine complex is too high, then the polymerization may proceed toorapidly to allow for effective mixing and use of the resultingcomposition. Large amounts of complex could also lead to the generationof large volumes of borane, which, in the case of an adhesive, couldweaken the bondline. The useful rate of polymerization will depend inpart on the method of applying the composition to a substrate. Thus, afaster rate of polymerization may be accommodated by using a high speedautomated industrial adhesive applicator rather than by applying thecomposition with a hand applicator or by manually mixing thecomposition.

Within these parameters, and in the particular case of an adhesive, aneffective amount of the organoborane polyamine complex is an amount thatpreferably provides about 0.03 to 1.5 weight % boron, based on the totalweight of the adhesive composition, more preferably about 0.1 to 0.3weight % boron.

The weight % of boron in a composition is equal to the following:##EQU1##

The organoborane polyamine complexes may be readily prepared using knowntechniques. Typically, the polyamine is combined with the organoboranein an inert atmosphere with slow stirring. An exotherm is often observedand cooling of the mixture is, therefore, recommended. If theingredients have a high vapor pressure, it is desirable to keep thereaction temperature below about 70° to 80° C. Once the materials havebeen well mixed the complex is permitted to cool to room temperature. Nospecial storage conditions are required although it is preferred thatthe complex be kept in a capped vessel in a cool, dark location.Advantageously, the complexes of the invention can be prepared in theabsence of organic solvents that would later have to be removed,although they could be prepared in solvent if so desired. Solvents usedin the preparation of the complexes should, preferably, be ones that donot coordinate amines, for example, tetrahydrofuran or hexane.

Advantageously, the preferred organoborane polyamine complexes of theinvention are air stable. By "air stable" it is meant that when thecomplexes are stored in a capped vessel at room temperature (about 20°to 22° C.) and under otherwise ambient conditions (i.e., not under avacuum and not in an inert atmosphere), the complexes remain useful aspolymerization initiators for at least about two weeks, although thecomplexes may be readily stored under these conditions for many monthsand up to a year or more. By "air stable" it is also meant that thecomplexes are not pyrophoric, as explained more fully hereinbelow. Theair stability of the complex is enhanced when the complex is acrystalline material. However, the complexes of the invention are airstable for at least six months even when they are liquids. Liquidcomplexes are easier to handle and mix than are crystalline complexes.

As noted above, the organoborane polyamine complexes of the inventionare especially useful as polymerization initiators, in particular, forinitiating the polymerization of acrylic monomers. In such cases, theorganoborane polyamine complexes form one component of a polymerizationinitiator system that comprises and, more preferably, consistsessentially of an effective amount of the organoborane polyamine complexand an effective amount of a compound that is reactive with amine forliberating organoborane so as to initiate polymerization.

The amine reactive compound liberates organoborane by reacting with thepolyamine, thereby removing the organoborane from chemical attachmentwith the polyamine. A wide variety of materials may be used to providethe amine reactive compound. Desirable amine reactive compounds arethose materials that can readily form reaction products with amines ator below (and, more preferably, at) room temperature (about 20° to 22°C.) so as to provide a composition such as an adhesive that can beeasily used and cured under ambient conditions. General classes of suchcompounds include isocyanate, acid chloride, sulfonyl chloride,aldehyde, and the like. Particular examples of compounds falling withinthese general classes include toluene diisocyanate, benzaldehyde, andmethacryloyl chloride.

The amine reactive compound is employed in an effective amount; that is,an amount effective to promote polymerization by liberating organoboranefrom the complex but without materially adversely affecting theproperties of the ultimate polymerized composition. Larger amounts ofamine reactive compound may permit the polymerization to proceed tooquickly and, in the case of adhesives, the resulting materials maydemonstrate inadequate adhesion to low energy surfaces. Undesirable sidereactions that adversely affect the performance properties of thepolymerized composition, or an undesirably high level of extractables inthe polymerized composition may also result from using large amounts ofamine reactive compound. On the other hand, an excess of certain aminereactive compounds may promote adhesion to higher energy surfaces. Ifsmall amounts of amine reactive compound are employed, the rate ofpolymerization may be too slow and the monomers that are beingpolymerized may not adequately increase in molecular weight. However, areduced amount of amine reactive compound may be helpful in slowing therate of polymerization if it is otherwise too fast.

Within these parameters, the amine reactive compound may be provided inan amount wherein the number of equivalents of amine reactive groups isas much as twice stoichiometric with the number of amine groups in theorganoborane polyamine complex. However, it is much more preferred thatthe number of equivalents of amine reactive groups be stoichiometricwith the number of amine groups in the organoborane polyamine complex.

Acids may also be used as the amine reactive compound. Any acid that canliberate the organoborane by salting the polyamine group may beemployed. Useful acids include Lewis acids (e.g., SnCl₄, TICl₄ and thelike) and Bronsted acids such as those having the general formula R⁸--COOH, where R⁸ is hydrogen, an alkenyl group of 1 to 8 and preferably1 to 4 carbon atoms, or an aryl group of 6 to 10, preferably 6 to 8carbon atoms. The alkenyl groups may comprise a straight chain or theymay be branched. They may be saturated or unsaturated. The aryl groupsmay contain substituents such as alkyl, alkoxy or halogen moieties.Illustrative acids of this type include acrylic acid, methacrylic acid,acetic acid, benzoic acid, and p-methoxybenzoic acid. Other usefulBronsted acids include HCl, H₂ SO₄, H₃ PO₄ and the like. Acrylic acidand methacrylic acid are preferred.

Somewhat different formulating is preferred with acids which,preferably, are provided in an amount of about 100 to 350 mole % basedon the number of equivalents of amine groups, moieties or functionalitypresent in the complex, more preferably about 150 to 250 mole %.

The organoborane polyamine complex initiator systems of the inventionare especially useful in polymerizing acrylic monomers, particularly formaking polymerizable acrylic adhesives. By "acrylic monomer" is meantpolymerizable monomers having one or more acrylic or substituted acrylicmoieties, chemical groups or functionality; that is, groups having thegeneral structure ##STR4## wherein R is hydrogen or an organic radicaland R' is an organic radical. Where R and R' are organic radicals, theymay be the same or they may be different. Blends of acrylic monomers mayalso be used. The polymerizable acrylic monomer may be monofunctional,polyfunctional or a combination thereof.

The most useful monomers are monofunctional acrylate and methacrylateesters and substituted derivatives thereof such as hydroxy, amide,cyano, chloro, and silane derivatives as well as blends of substitutedand unsubstituted monofunctional acrylate and methacrylate esters.Particularly preferred monomers include lower molecular weightmethacrylate esters such as methyl methacrylate, ethyl methacrylate,methoxy ethyl methacrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate,and blends thereof.

Both acrylate esters and higher molecular weight methacrylate esters areless preferred for use alone, but can be especially usefully employed asmodifying monomers with predominating amounts of lower molecular weightmethacrylate esters so as to, for example, enhance the softness orflexibility of the ultimate composition. Examples of such acrylateesters and higher molecular weight methacrylate esters include methylacrylate, ethyl acrylate, isobornyl methacrylate, hydroxypropylacrylate, butyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate,2-ethylhexyl methacrylate, decylmethacrylate, dodecyl methacrylate,tert-butyl methacrylate, acrylamide, N-methyl acrylamide, diacetoneacrylamide, N-tert-butyl acrylamide, N-tert-octyl acrylamide,N-butoxyacrylamide, gamma-methacryloxypropyl trimethoxysilane,2-cyanoethyl acrylate, 3-cyanopropyl acrylate, tetrahydrofurfurylchloroacrylate, glycidyl acrylate, glycidyl methacrylate, and the like.Dimethylaminoethyl acrylate and dimethylamino methacrylate may also beused as modifying agents although the additional amine functionality mayrequire a larger amount of amine reactive compound.

Particularly preferred are blends of any of the lower molecular weightalkyl methacrylate esters described above with alkyl acrylates having 4to 10 carbon atoms in the alkyl group, such as blends of methylmethacrylate and butylacrylate. Polymerizable compositions of this typemay broadly comprise, based on the total weight of the composition,about 2 to 40 wt. % of the alkyl acrylate and, correspondingly, about 60to 98 wt. % of the alkyl methacrylate.

Another class of polymerizable monomers that are especially useful asmodifiers, such as for improving the creep resistance or temperatureresistance of the ultimate composition, corresponds to the generalformula: ##STR5## R⁹ may be selected from the group consisting ofhydrogen methyl, ethyl, --CH₂ OH, and ##STR6## R¹⁰ may be selected fromthe group consisting of chlorine, methyl and ethyl. R¹¹ may be selectedfrom the group consisting of hydrogen, hydroxy, and ##STR7## The valueof a is an integer greater than or equal to 1, more preferably, from 1to about 8, and most preferably from 1 to 4. The integral value of b isgreater than or equal to 1, more preferably, from 1 to about 20. Thevalue of c is 0 or 1.

Other acrylic monomers useful with the polymerization initiator systems,especially as modifying monomers, include ethylene glycoldimethacrylate, ethylene glycol diacrylate, polyethylene glycoldiacrylate, tetraethylene glycol dimethacrylate, diglycerol diacrylate,diethylene glycol dimethacrylate, pentaerythritol triacrylate,trimethylolpropane trimethacrylate, as well as other polyetherdiacrylates and dimethacrylates.

Other polymerizable monomers that are useful in the invention,particularly as modifying monomers, have the general formula: ##STR8##R¹² may be hydrogen, chlorine, methyl or ethyl; R¹³ may be an alkylenegroup with 2 to 6 carbon atoms; and R¹⁴ is (CH₂)_(e) in which e is aninteger of 0 to 8, or one of the following: ##STR9## the phenyl groupbeing substitutable at any one of the ortho, meta or para positions. Thevalue of d is an integer of 1 to 4.

Typical monomers of this class include dimethacrylate of bis(ethyleneglycol) adipate, dimethacrylate of bis(ethylene glycol) maleate,dimethacrylate of bis(ethylene glycol) phthalate, dimethacrylate ofbis(tetraethylene glycol) phthalate, dimethacrylate of bis(tetraethyleneglycol) sebacate, dimethacrylates of bis(tetraethylene glycol) maleate,and the diacrylates and chloroacrylates corresponding to thedimethacrylates, and the like.

Also useful as modifying agents are monomers that areisocyanate-hydroxyacrylate or isocyanate-aminoacrylate reactionproducts. These may be characterized as acrylate terminatedpolyurethanes and polyureides or polyureas. Such monomers have thefollowing general formula: ##STR10## where X is selected from the groupconsisting of --O--and ##STR11## R¹⁵ is selected from the groupconsisting of hydrogen and lower alkyl groups (e.g., 1 to 7 carbonatoms). T is the organic residue of an active hydrogen-containingacrylic ester, the active hydrogen having been removed and the esterbeing hydroxy or amino substituted on the alkyl portion thereof(including the methyl, ethyl and chlorine homologs). The integral valueof f is from 1 to 6. L is a mono- or polyvalent organic radical selectedfrom the group consisting of alkyl, alkylene, alkenyl, cycloalkyl,cycloalkylene, aryl, aralkyl, alkaryl, poly(oxyalkylene),poly(carboalkoxyalkylene), and heterocyclic radicals, both substitutedand unsubstituted.

Typical monomers of this class include the reaction product of mono- orpolyisocyanates, for example, toluene diisocyanate, with an acrylateester containing a hydroxy or an amino group in the non-acrylate portionthereof, for example, hydroxyethyl methacrylate.

Still another class of modifying monomers useful in the presentinvention are the mono- and polyacrylate and methacrylate esters ofbisphenol type compounds. These monomers may be described by thefollowing formula: ##STR12## where R¹⁶ is methyl, ethyl, carboxyalkyl orhydrogen; R¹⁷ is hydrogen, methyl or ethyl; R¹⁸ is hydrogen, methyl orhydroxyl; R¹⁹ is hydrogen, chlorine, methyl or ethyl; and g is aninteger having a value of 0 to 8. Representative monomers of theabove-described class include dimethacrylate and diacrylate esters of4,4'-bis-hydroxyethoxy-bisphenol A, dimethacrylate and diacrylate estersof bisphenol A, etc.

The compositions may further comprise a variety of optional additives.One particularly useful additive is a thickener such as a medium (e.g.,about 100,000) molecular weight polymethyl methacrylate which may beincorporated in an amount of about 10 to 40 weight %, based on the totalweight of the composition. Thickeners may be employed to increase theviscosity of the composition to a more easily applied viscous syrup-likeconsistency.

Another particularly useful additive is an elastomeric material. Thesematerials can improve the fracture toughness of compositions madetherewith which can be beneficial when, for example, bonding stiff, highyield strength materials such as metal substrates that do notmechanically absorb energy as easily as other materials, such asflexible polymeric substrates. Such additives can be incorporated in anamount of about 5% to 35% by weight, based on the total weight of thecomposition.

Useful elastomeric modifiers include chlorinated or chlorosulphonatedpolyethylenes such as HYPALON 30 (commercially available from E. I.dupont de Nemours and Co., Wilmington Del.). Also useful, and even morepreferred, are certain graft copolymer resins such as particles thatcomprise rubber or rubber-like cores or networks that are surrounded byrelatively hard shells, these materials often being referred to as"core-shell" polymers. Most preferred are theacrylonitrile-butadiene-styrene graft copolymers.

In addition to improving the fracture toughness of the composition,core-shell polymers can also impart enhanced spreading and flowproperties to the uncured composition. These enhanced properties may bemanifested by a reduced tendency for the composition to leave anundesirable "string" upon dispensing from a syringe-type applicator, orsag or slump after having been applied to a vertical surface. Use ofmore than about 20% of a core-shell polymer additive is desirable forachieving improved sag-slump resistance.

Another useful adjuvant is a crosslinking agent. Crosslinking agents canbe used to enhance the solvent resistance of the adhesive bond, althoughcertain compositions of the invention have good solvent resistance evenin the absence of externally added crosslinking agents. Typicallyemployed in an amount of about 0.2 to 10 weight % based on the totalweight of the composition, useful crosslinkers include the variousdiacrylates referred to above as possible acrylic modifying monomers aswell as other materials. Particular examples of suitable crosslinkingagents include ethylene glycol dimethacrylate, ethylene glycoldiacrylate, triethyleneglycol dimethacrylate, diethylene glycolbismethacryloxy carbonate, polyethylene glycol diacrylate, tetraethyleneglycol dimethacrylate, diglycerol diacrylate, diethylene glycoldimethacrylate, pentaerythritol triacrylate, trimethylolpropanetrimethacrylate, as well as other polyether diacrylates anddimethacrylates.

Peroxides may be optionally included (typically in an amount of about 2%by weight or less, based on the total weight of the composition), forexample, to adjust the speed at which the compositions polymerize or tocomplete the polymerization.

Small amounts of inhibitors such as hydroquinone may be used, forexample, to prevent or reduce degradation of the acrylic monomers duringstorage. Inhibitors may be added in an amount that does not materiallyreduce the rate of polymerization or the ultimate properties of anadhesive or other composition made therewith, typically about 100-10,000ppm based on the weight of the polymerizable monomers.

Other possible additives include non-reactive colorants, fillers (e.g.,carbon black), etc.

The various optional additives are employed in an amount that does notsignificantly adversely affect the polymerization process or the desiredproperties of compositions made therewith.

Polymerizable acrylic compositions according to the invention may beused in a wide variety of ways, including as sealants, coatings, andinjection molding resins. They may also be used as matrix resins inconjunction with glass and metal fiber mats such as in resin transfermolding operations. They may further be used as encapsulants and pottingcompounds such as in the manufacture of electrical components, printedcircuit boards and the like. Quite desirably, they provide polymerizableacrylic adhesive compositions that can bond a diverse myriad ofsubstrates, including polymers, wood, ceramics, concrete, and primedmetals.

Polymerizable acrylic compositions of the invention are especiallyuseful for adhesively bonding low surface energy plastic or polymericsubstrates that historically have been very difficult to bond withoutusing complicated surface preparation techniques, priming, etc. By lowsurface energy substrates is meant materials that have a surface energyof less than 45 mJ/m², more typically less than 40 mJ/m² or less than 35mJ/m². (The expression "surface energy" is often used synonymously with"critical wetting tension" by others.) Included among such materials arepolyethylene, polypropylene, acrylonitrile-butadiene-styrene, polyamide,and fluorinated polymers such as polytetrafluoroethylene (TEFLON) whichhas a surface energy of less than 20 mJ/m². Other polymers of somewhathigher surface energy that may be usefully bonded with the compositionsof the invention include polycarbonate, polymethylmethacrylate, andpolyvinylchloride.

The polymerizable compositions of the invention can be easily used astwo-part adhesives. The components of the polymerizable composition areblended as would normally be done when working with such materials. Theamine reactive component of the polymerization initiator system isusually included in this blend so as to separate it from theorganoborane polyamine complex, thus providing one part of the two-partcomposition. The organoborane polyamine complex of the polymerizationinitiator system provides the second part of the composition and isadded to the first part shortly before it is desired to use thecomposition. The complex may be added to the first part directly or itmay be predissolved in an appropriate carrier such as a small amount ofmethyl methacrylate.

While a nitrogen atom to boron atom ratio of about 1:1 in theorganoborane polyamine complex is preferred, it is desirable to storesuch complexes apart from the monomers to inhibit prematurepolymerization of the monomers. Complexes in which the nitrogen atom toboron atom ratio is greater than 1:1 may be sufficiently stable thatthey can be blended with acrylic monomer in useful proportions. However,in such situations, the presence of additional non-polymerizingreactants (e.g., the amine reactive compound) may result in other,undesirable affects.

For a two-part adhesive such as those of the invention to be most easilyused in commercial and industrial environments, the ratio at which thetwo parts are combined should be a convenient whole number. Thisfacilitates application of the adhesive with conventional, commerciallyavailable dispensers. Such dispensers are shown in U.S. Pat. Nos.4,538,920 and 5,082,147 and are available from Conprotec, Inc. (Salem,N.H.) under the tradename "Mixpac". Typically, these dispensers use apair of tubular receptacles arranged side-by-side with each tube beingintended to receive one of the two parts of the adhesive. Two plungers,one for each tube, are simultaneously advanced (e.g., manually or by ahand-actuated ratcheting mechanism) to evacuate the contents of thetubes into a common, hollow, elongated mixing chamber that may alsocontain a static mixer to facilitate blending of the two parts. Theblended adhesive is extruded from the mixing chamber onto a substrate.Once the tubes have been emptied, they can be replaced with fresh tubesand the application process continued.

The ratio at which the two parts of the adhesive are combined iscontrolled by the diameter of the tubes. (Each plunger is sized to bereceived within a tube of fixed diameter, and the plungers are advancedinto the tubes at the same speed.) A single dispenser is often intendedfor use with a variety of different two-part adhesives and the plungersare sized to deliver the two parts of the adhesive at a convenient mixratio. Some common mix ratios are 1:1, 2:1, 4:1 and 10:1.

If the two parts of the adhesive are combined in an odd mix ratio (e.g.100:3.5), then the ultimate user would probably manually weigh the twoparts of the adhesive. Thus, for best commercial and industrial utilityand for ease of use with currently available dispensing equipment, thetwo parts of the adhesive should be capable of being combined in acommon, whole number mix ratio such as 10:1 or less, more preferably4:1, 3:1, 2:1 or 1:1.

Adhesive compositions of the invention are uniquely suited for use withconventional, commercially available dispensing equipment for two-partadhesives. The organoborane polyamine complexes of the invention have arelatively high molecular weight (as compared to other knownorganoborane amine complexes). Consequently, the complex can compriseessentially all of the second part of the adhesive while still providingan effective amount of organoborane in a useful whole number mix ratioof 10:1 or less.

Once the two parts have been combined, the composition should be usedquickly, as the useful pot life may be short depending upon the acrylicmonomer mix, the amount of complex, and the temperature at which thebonding is to be performed.

The polymerizable composition is applied to one or both substrates andthen the substrates are joined together with pressure to force excesscomposition out of the bond line. This also has the advantage ofdisplacing composition that has been exposed to air and that may havebegun to oxidize. In general, the bonds should be made shortly after thecomposition has been applied, preferably within about 10 minutes. Thetypical bond line thickness is about 0.1 to 0.3 mm. The bonding processcan easily be carried out at room temperature and to improve the degreeof polymerization it is desirable to keep the temperature below about40° C., preferably below 30° C., and most preferably below about 25° C.

The bonds will cure to a reasonable green strength to permit handling ofthe bonded components within about 2 to 3 hours. Full strength will bereached in about 24 hours under ambient conditions; post-curing withheat (typically about 80° C.) may be used if desired.

When bonding fluoroplastics, it is advantageous to cool the first partof the two-part composition to about 0° to 5° C. before adding theorganoborane polyamine complex. The bond should be made as soon afterthe composition has been applied as practical; performing the bondingoperation at less than room temperature is also helpful.

The invention will be more fully appreciated with reference to thefollowing nonlimiting examples in which (unless noted otherwise) allweights are given as weight percents (weight %), based on the totalweight of the composition which is 100 weight %, and are reported to twosignificant digits following the decimal point.

Examples that were subsequently evaluated to measure the lap shearstrength of the adhesive bonds were tested as described below.

Lap Shear Strength Test Method

The test specimens used were similar to that described in ASTM D-1002except that the specimens were generated using finger panels of nominaldimensions 1 in.×4 in.×1/8 in. thick (2.5 cm×10.2 cm×0.3 cm thick). 0.5in. (1.3 cm) wide red lithographers tape was applied to the end of oneof the adherends in order to help fixture the bond and also to aid inmaking the lap region to be 0.5 in. (1.3 cm). Short pieces of 6 mil(0.15 mm) diameter piano wire were cut for use as spacers to control thethickness of the adhesive bondline.

The adhesive was prepared by weighing the monomer mixture into a vialthat was capable of being sealed with a poly cap. Organoborane polyamineinitiator complex was then added, blended with the monomer mixture usinga wooden stick, and the vial was sealed with the poly cap. In general,the addition of organoborane polyamine amine initiator complex to themonomer mixture caused the mixture to slightly exotherm and, in somecases, turn yellow. A dab of the mixed adhesive was applied to eachadherend and spread to make sure that a 1 in.×0.5 in. (2.5 cm×1.3 cm)area was covered at the end of each adherend. Two pieces of piano wirewere placed into the adhesive on one adherend and the bond was closedand fixtured with the lithographers tape. The bond was further fixturedwith two binder clips and allowed to cure at room temperature for 48hours at which time the binder clips and tape were removed.

Lap shear testing was done with three types of adherends: mechanicalgrade TEFLON, high density polyethylene, and polypropylene, as availablefrom Precision Punch and Plastic Co. (Minneapolis, Minn.). Threeadhesive bonds were made with each adherend and each adhesivecombination. For each adhesive, the TEFLON was bonded first, then thehigh density polyethylene, and then the polypropylene. After curing, thebonds were tested to failure using a Tensile Testing Machine. Thecrosshead speed was 0.1 in./minute (2.5 mm/min.) and the tests werecarried out at room temperature. Bonds were visually inspected afterbeing loaded to failure to determine the failure mode. Failure of theadherends is the most preferred although cohesive failure of thecomposition evidences a useful formulation.

Failure modes are reported in the examples based on a series of codedabbreviations which may be interpreted as follows:

    ______________________________________                                        Abbreviation  Failure Mode                                                    ______________________________________                                        a             Good filet adhesion                                             b             One or more bonds stretched to                                                yield of the adherend without                                                 failure                                                         c             Mixed mode failure                                              d             Failure of the adherend                                         e             Cohesive failure within the                                                   adhesive                                                        f             Adhesion failure of the adhesive                                g             Incomplete wetting; puddling of the                                           adhesive                                                        ______________________________________                                    

EXAMPLE 1

In example 1 organoborane polyamine complexes were synthesized. Allglassware was washed and fired at 1000° F. (538° C.) or was fired bymeans of a Bunsen burner until the glassware glowed orange. Apolyethylene glove bag was set up in the hood and was flushed withnitrogen. (In some cases, the synthesis was carried out in a glove boxwhich had been inserted with nitrogen.) The glove bag or glove boxcontained a pressure equalizing dropping funnel, an electric balance, aflask with appropriate stoppers, and a stand.

The polyoxyalkylenepolyamine was degassed by freeze-thaw cycles undervacuum and was then weighed into the flask. The organoborane was weighedinto the pressure equalizing dropping funnel and then added dropwise tothe polyamine with stirring and cooling. A mild exotherm was observedand the reaction mixture was alternately clear and cloudy. The additionof the organoborane was moderated to control the exotherm. In somecases, fuming occurred and the addition of the borane was slowed untilthe fuming had subsided. Once all of the organoborane had been added,the flask was allowed to equilibrate to room temperature until either aliquid or a crystalline mass was obtained. If a crystalline mass wasobtained, it was heated to 55° C. by means of an oil bath outside of theglove bag to liquify it so that it could be transferred. A hazy whiteliquid resulted which was poured into a vial previously flushed withnitrogen. After cooling, a white crystalline material was obtained. Ifthe result was not a crystalline mass, then the liquid was poured fromthe flask into a bottle and sealed.

Complexes were made with the organoboranes and polyamines that arelisted below in Table 1. For each complex the boron atom to nitrogenatom ratio was 1:1 (i.e., one mole of trialkyl borane for eachequivalent of amine functionality.)

The complexes were examined for pyrophoricity. Drops of liquid sampleswere placed on paper towels which were then placed in a fume hood. Thesamples were observed for 24 hours. Any ignition is noted in Table 1. Inone case, the catalyst did not ignite the paper towel until the paperwas rubbed against a waxed floor. Most of the organoborane polyaminecomplexes of the invention are air stable and do not ignite combustiblematerials.

                                      TABLE 1                                     __________________________________________________________________________                         Calculated                                                                    Molecular                                                                           Calculated                                         Complex         Organo-                                                                            Weight of                                                                           % Boron in                                                                          Appearance                                   Designation                                                                         Polyamine borane                                                                             the Complex                                                                         the Complex                                                                         of Complex                                                                            Comments                             __________________________________________________________________________    A     Diethylene glycol                                                                       Tri-n-                                                                             584   3.73  Clear yellowish                                                                       No ignition                                bis propyl amine                                                                        butyl            liquid                                             (H221)    borane                                                        B     Diethylene glycol                                                                       Tri-ethyl                                                                          416   5.24  Clear liquid                                                                          No ignition                                bis propyl amine                                                                        borane           which may                                          (H221)                     solidify                                     C     Polypropylene oxide                                                                     Tri-n-                                                                             594   3.67  Clear liquid                                                                          Smoked when                                diamine   butyl                    applied to paper                           (Jeffamine D-230)                                                                       borane                                                        D     Polypropylene oxide                                                                     Tri-ethyl                                                                          426   5.11  Clear liquid                                                                          Ignited paper                              diamine   borane                                                              (Jeffamine D-230)                                                       E     Polypropylene oxide                                                                     Tri-n-                                                                             768   2.84  Clear liquid                                                                          No ignition                                diamine   butyl                                                               (Jeffamine D-400)                                                                       borane                                                        F     Polypropylene oxide                                                                     Tri-ethyl                                                                          600   3.63  Clear yellowish                                                                       Ignited if liquid                          diamine   borane           liquid  was placed on paper                        (Jeffamine D-400)                  and then rubbed                                                               against a waxed floor                G     Poly(ethylene                                                                           Tri-ethyl                                                                          796   2.73  Clear liquid                                                                          No ignition                                oxide-    borane                                                              co-propylene oxide)                                                           diamine                                                                       (Jeffamine ED-600)                                                      H     Polypropylene oxide                                                                     Tri-n-                                                                             660   3.30  Waxy crystalline                                                                      No ignition                                diamine   butyl            solid                                              (Jeffamine EDR-148)                                                                     borane                                                        I     Polypropylene                                                                           Tri-n-                                                                             2364  0.92  Clear liquid                                                                          No ignition                                diamine   butyl                                                               (Jeffamine D-2000)                                                                      borane                                                        J     Polypropylene oxide                                                                     Tri-n-                                                                             5364  0.41  Clear liquid                                                                          No ignition                                diamine   butyl                                                               (Jeffamine D-5000)                                                                      borane                                                        K     Polypropylene oxide                                                                     Tri-ethyl                                                                          636   3.42  Clear, yellowish,                                                                     No ignition                                triamine  borane           viscous liquid                                     (Jeffamine T-403)                                                       __________________________________________________________________________

(H221 is commercially available from Union Carbide Company. The"Jeffamine" line of products is commercially available from HuntsmanChemical Company.)

EXAMPLE 2

A series of adhesive compositions was prepared using different complexesfrom Table 1 (each based on tri-n-butyl borane) and the followingmonomer mixture: 78 g of methyl methacrylate, 56 g of n-butyl acrylate,60 g of medium molecular weight poly(methyl methacrylate)(101,000molecular weight poly(methyl methacrylate-co-ethylacrylate) with lessthan 5% ethylacrylate from Aldrich Chemical Co.), and 6 g of methacrylicacid. The components of the monomer mixture were weighed into a 1 quartbrown bottle that was then sealed and placed overnight in aLaunder-o-meter that was set to 55° C. A light yellow to white, clear,moderately viscous solution resulted. This is referred to as MonomerMixture A.

Using the techniques described above, 5 g of Monomer Mixture A werecombined with various organoborane polyamine complexes to provideadhesive compositions that were tested for lap shear strength. In eachcase the complex provided about 0.2% by weight boron in the adhesive.The results are reported in Table 2 in pounds per square inch (psi).

                                      TABLE 2                                     __________________________________________________________________________                 Weight %                                                               Complex                                                                              Boron in the                                                                        Lap Shear to                                                                         Lap Shear to                                                                        Lap Shear to                                  Complex                                                                             Amount Adhesive                                                                            TEFLON Polyethylene                                                                        Polypropylene                                 Designation                                                                         (g)    Composition                                                                         (psi)  (psi) (psi)                                         __________________________________________________________________________    C     0.311  0.22  374    458   831                                           A     0.299  0.21  324    781   646                                           H     0.262  0.21  230    800   751                                           __________________________________________________________________________

Example 2 shows that the organoborane polyamine complexes of theinvention can be used to prepare acrylic adhesive compositions thatprovide high strength bonds to low surface energy plastic substrates. Insome cases the lap shear strength exceeded the yield strength of thesubstrate.

EXAMPLE 3

Using the techniques described above, 5 g of Monomer Mixture A (seeexample 2) were combined with various organoborane polyamine complexesfrom Table 1 to provide adhesive compositions that were tested for lapshear strength. In each case the complex provided about 0.26% by weightboron in the adhesive and the complex was based on triethylborane ratherthan tri-n-butylborane as used in example 2. The results are reportedbelow in Table 3.

                                      TABLE 3                                     __________________________________________________________________________          Complex                                                                            Lap Shear to                                                                             Lap Shear to                                                                             Lap Shear to                                 Complex                                                                             Amount                                                                             TEFLON                                                                              Mode of                                                                            Polyethylene                                                                        Mode of                                                                            Polypropylene                                                                        Mode of                               Designation                                                                         (g)  (psi) Failure                                                                            (psi) Failure                                                                            (psi)  Failure                               __________________________________________________________________________    B     0.262                                                                              310   a,c  764   e    772    d                                     D     0.269                                                                              322   a,c  742   e    558    e                                     F     0.379                                                                              344   b,a  730   e    484    e                                     __________________________________________________________________________

Table 3 indicates that useful adhesive compositions can also be madewhen the organoborane is triethylborane.

EXAMPLE 4

Organoborane polyamine complexes are prone to degradation during storagedue to possible oxidation of the organoborane. However, as shown below,the complexes of the invention demonstrate excellent storage stability,even when kept under ambient, room temperature conditions for as long assix months.

More specifically, adhesive compositions similar to those in example 2were prepared as described above except using organoborane polyaminecomplexes that had first been stored under ambient, room temperatureconditions for about 6 months. Each example was based on 5 g of MonomerMixture A and an amount of complex sufficient to provide about 0.21% byweight boron to the adhesive composition. The adhesive compositions werethen prepared and tested as described in conjunction with example 2,with the results shown below in Table 4.

                                      TABLE 4                                     __________________________________________________________________________          Amount of                                                                          Lap Shear to                                                                             Lap Shear to                                                                             Lap Shear to                                 Complex                                                                             Complex                                                                            TEFLON                                                                              Mode of                                                                            Polyethylene                                                                        Mode of                                                                            Polypropylene                                                                        Mode of                               Designation                                                                         (g)  (psi) Failure                                                                            (psi) Failure                                                                            (psi)  Failure                               __________________________________________________________________________    A     0.305                                                                              186   a,f  676   e    416    a,c                                   H     0.267                                                                              190   a,f  722   e    376    a,c                                   C     0.317                                                                              230   a,f  652   e    484    e,d                                   __________________________________________________________________________

The good adhesive performance evidenced by Table 4 was promoted byseparately storing the monomers and the complex.

EXAMPLE 5

Using the methods described above, Monomer Mixture A (see example 2) wascombined with various organoborane polyamine complexes from Table 1 toprovide adhesive compositions that were tested for lap shear strength.In each case the complex and the monomer mix were blended at a weightratio of 10:1 (i.e., 5 g Monomer Mixture A+0.5 g complex). The resultsare reported in Table 5.

                                      TABLE 5                                     __________________________________________________________________________          Lap Shear to                                                                        Wt. %     Lap Shear to                                                                             Lap Shear to                                 Complex                                                                             TEFLON                                                                              Boron in                                                                           Mode of                                                                            Polyethylene                                                                        Mode of                                                                            Polypropylene                                                                        Mode of                               Designation                                                                         (psi) Adhesive                                                                           Failure                                                                            (psi) Failure                                                                            (psi)  Failure                               __________________________________________________________________________    A     140   0.34 a,f  714   e    266    a,f                                   E     180   0.26 a,c  710   e    520    d,a,c                                 C     126   0.33 c    688   e    340    a,c                                   B     250   0.47 a,c  712   e    322    c                                     F     314   0.33 a,e  612   e    598    a,e                                   D     286   0.47 a    742   e    566    e                                     __________________________________________________________________________

Table 5 shows that adhesive compositions according to the invention andwhich provide acceptable bond strengths and failure modes can beobtained when organoborane polyamine complexes are combined with acrylicmonomers in an industrially useful 10:1 mix ratio.

EXAMPLE 6

In example 6, 5 g of Monomer Mix A were combined with different amountsof organoborane polyamine complexes B, F and K to vary the level ofboron in the adhesive composition from 0.015% to 0.24%. The compositionswere prepared and tested for lap shear strength using the techniquesdescribed above and with the results shown below in Table 6.

                                      TABLE 6                                     __________________________________________________________________________               Weight %                                                                 Amount of                                                                          Boron in                                                                            Lap Shear on                                                                             Lap Shear on                                                                             Lap Shear on                           Complex                                                                             Complex                                                                            the Adhesive                                                                        TEFLON                                                                              Mode of                                                                            Polyethylene                                                                        Mode of                                                                            Polypropylene                                                                        Mode of                         Designation                                                                         (g)  Composition                                                                         (psi) Failure                                                                            (psi) Failure                                                                            (psi)  Failure                         __________________________________________________________________________    B     0.0144                                                                             0.015 1.3   f,g  2     f,g  6      f,g                             B     0.0385                                                                             0.040 2.7   c,g  163   c,e,g                                                                              305    c,e,g                           B     0.0974                                                                             0.10  348   a,b,e                                                                              576   a,e  586    a,e                             B     0.236                                                                              0.24  342   a,b,e                                                                              642   a,e  516    a,e                             F     0.0207                                                                             0.015 0     f,g  2.7   f,g  5.3    f,g                             F     0.0557                                                                             0.040 200   c,e  352   a,e  380    a,e                             F     0.141                                                                              0.10  342   a,b,e                                                                              468   a,e  464    a,d,e                           F     0.347                                                                              0.24  290   a,e  550   a,e  474    a,e                             K     0.0182                                                                             0.012 2     f,g  4     f,g  1.3    f,g                             K     0.0489                                                                             0.033 197   c,e,g                                                                              152   c,e,g                                                                              74     c,e,g                           K     0.124                                                                              0.83  355   b    324   a,c,e                                                                              505    a,e                             K     0.292                                                                              0.19  347   a,b,e                                                                              204   a,c,e                                                                              477    a,e                             __________________________________________________________________________

Example 6 shows the effect on adhesion to low surface energy plasticswhen the level of boron in the adhesive composition is varied. Adhesivecompositions according to the invention preferably include about 0.03 to1.5 weight % boron based on the total weight of the adhesivecomposition, more preferably about 0.04 to 1.0 weight %, and mostpreferably about 0.1 to 0.3 weight %. When the weight % boron is too low(i.e., less than 0.03 weight %), minimal adhesion is obtained to lowsurface energy plastics. At high levels of boron (e.g., higher thanthose used in example 6), adhesion is still good but the adhesivebecomes increasingly porous due to the liberation of borane and, hence,are less desirable.

EXAMPLE 7

Example 7 describes the performance of a pair of known two-part acrylicadhesives, "DP-805" which is commercially available from the 3M Company(St. Paul, Minn.), and an adhesive that is intended to be based on U.S.Pat. No. 4,536,546, example 5 but using currently available materials(referred to herein as adhesive X). The formulation of adhesive X is asfollows:

Part A:

35.5 parts HYPALON 30 (from E.I. dupont de Nemours)

53.2 parts methyl methacrylate

9.8 parts methacrylic acid

1 part cumene hydroperoxide

Part B:

25 parts BLENDEX B467 (acrylonitrile-butadienestyrene terpolymer fromGeneral Electric Specialty Chemicals, Parkersburg, W. Va.)

75 parts methyl methacrylate

4.995 parts VANAX 808 (from Vanderbilt Chemical Co.)

0.005 part copper napthenate solution

Part A was generated by mixing the components until a viscous solutionresulted. Part B was generated by first mixing the graft co-polymer andthe methyl methacrylate until a stable bluish dispersion resulted. TheVANAX 808 and copper napthenate were then added. Adhesive bonds weremade and tested for lap shear strength as described in conjunction withexample 2 with the exception bonds were also made on 2024-T3 aluminumsubstrates according to the method described in ASTM D-1002. The resultsare shown below in Table 7.

                  TABLE 7                                                         ______________________________________                                                          DP-805                                                                              Adhesive X                                            ______________________________________                                        Lap Shear on Aluminum (psi)                                                                       3288    3688                                              Lap Shear on TEFLON (psi)                                                                         26      17                                                Lap Shear on Polyethylene (psi)                                                                   18      12                                                Lap Shear on Polypropylene (psi)                                                                  2.7     16                                                ______________________________________                                    

Table 7 shows that two-part acrylic adhesive compositions according tothe invention which include an effective amount of boron (as provided bythe organoborane polyamine complexes of the invention) have excellentadhesion to low surface energy plastics whereas other known two-partacrylic adhesives do not. However, the known adhesives do provide goodadhesion to aluminum substrates. The known adhesives suffered cohesivefailure with the aluminum substrates but failed adhesively with thepolymeric substrates.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of the invention. It should be understood that this inventionis not limited to the illustrative embodiments set forth herein.

The embodiments for which an exclusive property or privilege is claimedare defined as follows:
 1. A polymerizable acrylic compositioncomprising:a) at least one acrylic monomer; b) an effective amount of acomplex comprising organoborane and polyoxyalkylenepolyamine; and c) aneffective amount of a compound that is reactive with amine forliberating the organoborane to initiate polymerization of the at leastone acrylic monomer.
 2. A polymerizable acrylic composition according toclaim 1 wherein the at least one acrylic monomer is selected from thegroup consisting of monofunctional acrylate ester, monofunctionalmethacrylate ester, substituted derivatives of the foregoing, and blendsof the foregoing.
 3. A polymerizable acrylic composition according toclaim 2 wherein the monofunctional methacrylate ester is selected fromthe group consisting of methyl methacrylate, ethyl methacrylate, methoxyethyl methacrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate,and blends thereof.
 4. A polymerizable acrylic composition according toclaim 1 wherein the at least one acrylic monomer comprises a blend ofalkyl methacrylate and alkyl acrylate.
 5. A polymerizable acryliccomposition according to claim 4 wherein the alkyl methacrylate ismethyl methacrylate and the alkyl acrylate is butyl acrylate.
 6. Apolymerizable acrylic composition according to claim 1 furthercomprising an elastomeric modifier.
 7. A polymerizable acryliccomposition according to claim 1 wherein the composition comprises about0.03 to 1.5 weight % boron.
 8. A polymerizable acrylic compositionaccording to claim 7 wherein the composition comprises about 0.1 to 0.3weight % boron.
 9. A polymerizable acrylic composition according toclaim 1 wherein the compound that is reactive with amine is selectedfrom the group consisting of acid, isocyanate, acid chloride, sulfonylchloride, and aldehyde.
 10. A polymerizable acrylic compositionaccording to claim 1 wherein the complex has the structure ##STR13##wherein: R¹ is an alkyl group having 1 to 10 carbon atoms;R² and R³ areindependently selected from alkyl groups having 1 to 10 carbon atoms andphenyl-containing groups; Am is polyoxyalkylenepolyamine and has astructure selected from the group consisting of

    H.sub.2 NR.sup.4 O--(R.sup.5 O).sub.w --(R.sup.6 O).sub.x --(R.sup.5 O).sub.y --R.sup.4 NH.sub.2 and  H.sub.2 NR.sup.4 O--(R.sup.5 O).sub.w !.sub.z --R.sup.7,

wherein: R⁴, R⁵, and R⁶ are alkylene groups having 1 to 10 carbon atomsand which may be the same or which may be different; R⁷ is the residueof a polyol; w is ≧1; x is ≧0; y is ≧0; z is >2; and the value of v isselected so as to provide an effective ratio of boron atoms to nitrogenatoms in the complex.
 11. A polymerizable acrylic composition accordingto claim 10 wherein the compound that is reactive with amine is an acid.12. A polymerizable composition according to claim 11 wherein the acidis a Lewis acid or a carboxylic acid.
 13. A polymerizable acryliccomposition according to claim 10 wherein the compound reactive withamine is acrylic acid or methacrylic acid.
 14. A polymerizable acryliccomposition according to claim 1 that is an adhesive composition.
 15. Apolymerizable acrylic composition according to claim 14 that is atwo-part adhesive composition.
 16. A polymerizable acrylic compositionaccording to claim 15 wherein the first part of the two-part adhesivecomposition includes the at least one acrylic monomer and the compoundthat is reactive with amine, and the second part of the two-partadhesive composition includes the complex comprising organoborane andpolyoxyalkylenepolyamine.
 17. A polymerizable acrylic compositionaccording to claim 16 wherein the first and second parts of the two-partadhesive composition are retained by separate receptacles of a two-partadhesive dispenser.
 18. A polymerizable acrylic composition according toclaim 17 wherein the two-part adhesive dispenser is adapted to combinethe first part and the second part of the two-part adhesive compositionin a whole number mix ratio of 10:1 or less.
 19. A polymerizable acryliccomposition according to claim 18 wherein the two-part adhesivedispenser is adapted to combine the first part and the second part ofthe two-part adhesive composition in a whole number mix ratio of 4:1 orless.
 20. A polymerizable acrylic composition comprising:a) a blend ofacrylic monomers comprising alkyl acrylate monomer and alkylmethacrylate monomer; b) an organoborane polyamine complex having thestructure ##STR14## wherein: R¹ is an alkyl group having 1 to 10 carbonatoms; R² and R³ are independently selected from alkyl groups having 1to 10 carbon atoms and phenyl-containing groups; Am ispolyoxyalkylenepolyamine and has a structure selected from the groupconsisting of

    H.sub.2 NR.sup.4 O--(R.sup.5 O).sub.w --(R.sup.6 O).sub.x --(R.sup.5 O).sub.y --R.sup.4 NH.sub.2 and  H.sub.2 NR.sup.4 O--(R.sup.5 O).sub.w !.sub.z --R.sup.7,

wherein: R⁴, R⁵, and R⁶ are alkylene groups having 1 to 10 carbon atomsand which may be the same or which may be different; R⁷ is the residueof a polyol; the values of w, x, and y are selected such that theorganoborane polyamine complex is a liquid at room temperature; z is 3or 4; and the value of v is selected such that the ratio of nitrogenatoms to boron atoms in the complex is about 1:1 to 2:1; and; c) aneffective amount of acrylic acid or methacrylic acid for liberating theorganorborane in the complex to initiate polymerization of the acrylicmonomer.
 21. A polymerizable acrylic composition according to claim 20comprising about 0.03 to 1.5 weight % boron.
 22. A polymerizable acryliccomposition according to claim 21 comprising about 0.1 to 0.3 weight %boron.
 23. A method of initiating the polymerization of an acrylicmonomer, the method comprising the steps of:a) providing at least oneacrylic monomer; b) blending the at least one acrylic monomer with apolymerization initiator system comprising: i) a complex comprisingorganoborane and polyoxyalkylenepolyamine; and ii) an effective amountof a compound that is reactive with amine for liberating theorganoborane to initiate polymerization of the at least one acrylicmonomer; and c) initiating polymerization of the at least one acrylicmonomer.